Visio Blog - VSDX: the new Visio file format

tbd if this will ever fully find its way into Open XML -- it does use the Open Packaging Conventions (ISO/IEC 29500-2:2008) standard -- but it's great news for developers who want to use XML and work with Visio files

"Visio 2003, 2007 and 2010 all had the same primary Visio Drawing (VSD) file format. For most users, this was great: files could be shared easily between these three versions of Visio.
There were, however, some drawbacks. Most notably, the primary format was binary, which limited both the information stored in the file and how easily IT professionals and developers could work with it. For example, it was difficult for third parties to access and extract data from the binary format for use outside of Visio.
For the new Visio, we introduced an XML-based file format to provide new capabilities in Visio and improve interoperability with other applications."

Visio Blog - VSDX: the new Visio file format